According to EWI researcher Edward Herderick, the disaster at the Fukushima Daiichi nuclear power plant presents a key question to the materials community. He asks, “Are there materials innovations that can profoundly improve the safety of existing light water reactors?”

EWI has been testing the silicon carbide ceramic-matrix composites as replacements for the currently used zirconium alloy fuel cladding in light water reactors. While the SiC cladding would not have prevented the Japanese disaster, it might have prevented some of the cascading of problems seen in Japan, including the deterioration of the zirconium cladding (an event that eventually contributed to the chemical reactions that resulted in the explosions at the Fukushima reactor).

Making a SiC tube to hold nuclear fuel pellets is the relatively easy part of the solution. The difficulty has been with finding a way to join the SiC cap to the rest of the SiC tube so that the overall mechanical and thermal strength is not compromised.

“Joining” is one of the specialties of EWI, and that is how Herderick became involved. He and others at EWI perfected an approach that uses a multiphase braze alloy consisting predominately of silicon and aluminum and small amounts of alloying elements with a two-phase joined microstructure.

Samples of the EWI tubes were tested in an MIT research reactor, where they recently emerged intact, having survived six months of aggressive irradiation testing.

More testing is ahead, but Herderick says the use of the SiC tubes could lead to a substantial increase in existing reactor safety. “Transitioning from zirconium alloy nuclear fuel cladding to a silicon carbide composite cladding is fundamentally a materials challenge, and it would represent the biggest shift in light water reactor materials technology since their original design and introduction,” he says.